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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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454                                ALASKAN GLACIER STUDIES
race which slopes gradually southward from the mouth of Hanagita Valley. Young gorges have been cut across the remnants of this bench by tributary streams. Its top has the rounded outlines of a glaciated surface. Near the southern portion glacial gravels rest upon it.
The isolated 2200 foot rock hill called The Peninsula (PL CLXXIX), and a similar hillock just south of Cleave Creek, present interesting problems, deserving of attention, in connection with former marginal drainage and glacier distribution.
The Origin of Wood Canyon. Wood Canyon is a young, steep-sided gorge of a sort seen nowhere else in the lower Copper River. Its origin is interesting and may possibly be of importance in connection with the problem of how Copper River acquired its present course across the Chugach Range. This problem has been touched upon by Schrader and Spencer,1 and by Mendenhall.2
Without going in detail into this larger problem, which requires further field work in relation to several other outlets of the Copper-Susitna basin, it may be pointed out that a glacial origin 8 seems more reasonable than headwater erosion, as suggested by Mendenhall, or an antecedent origin for the course of Copper River through this northern portion of the mountains, with the Wood Canyon interpreted, as has been done by Schrader and Spencer, as an evidence of recent warping.
This hypothesis of glacial origin of the course of Copper River across the mountain range may be outlined as follows: The preglacial upper Copper and Chitina Rivers are thought of as having some other course to the sea than the present one. The preglacial lower Copper River is thought of as heading somewhere south of but close to the present Wood Canyon. A former subsequent stream in the Hanagita Valley is thought of as turning at right angles at the south end of what is now Wood Canyon and flowing northward through the pass, alluded to hereafter as Hanagita Watergap, to Chitina River, just as Tebay River fifteen miles farther east, now flows northward from Hanagita Valley to Chitina River.4 The hypothesis then supposes that the inter-montane glacier of the Copper River basin rose high enough to have an outlet southward through the Chugach Mountains by way of the lower Copper River, and that a glacial stream cut the present Wood Canyon and diverted the drainage of the eastern portion of the Copper River basin, that is the Upper Copper and Chitina Rivers, into the headwaters of the lower Copper, whose valley had been enlarged by glacial erosion to the present canyon form.
The conditions at Wood Canyon are as follows. The canyon is a narrow gash (PL CLXXVI, A) cut in the bottom of an older col. This broad flat-bottomed col, Hanagita Watergap, seems to be a preglacial stream course at a little higher level than the broad rock terrace in which the present gorge of the adjacent Chitina River is in-
1 Schrader, F. C., A Reconnaissance of a Part of Prince William Sound and the Copper River District* Alaska, in 1898, 20th Ann. Rept., U. S. Geol. Survey, Part VII, 1900, pp. 395-403; Schrader, F. C. and Spencer, A. C., Geology and Mineral Resources of a Portion of the Copper River District, House Doc. 546, 56th Congress, 2nd Session, Washington, 1901, pp. 70-75; Spencer, A. C., Pacific Mountain System in British Columbia and Alaska, Bull. Geol. Soc. Amer.. Vol. XIV, 1903, pp. 120-121, 127.
» Mendenhall, W. C., A Reconnaissance from Resurrection Bay to the Tanana River, Alaska, in 1898, 20th, Ann. Rept., U. S. Geol. Survey, Part VIE, 1900, pp. 334-385.
i Martin, Lawrence, Nat. Geog. Mag., Vol. XXTI, 1911, p. 560; Petermanns Geog. MitteUungen, Jahrgang, 1912, p. 81; The Canyon and Delta of the Copper River in Alaska, Bull, Geol. Soc. Amer.: Vol. 24, 1913.
«See PI. I., Bull. 374, U, S. Geol. Survey, 1909.